llvm-project/mlir/lib/Transforms/LowerAffine.cpp

539 lines
21 KiB
C++

//===- LowerAffine.cpp - Lower affine constructs to primitives ------------===//
//
// Copyright 2019 The MLIR Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// =============================================================================
//
// This file lowers affine constructs (If and For statements, AffineApply
// operations) within a function into their standard If and For equivalent ops.
//
//===----------------------------------------------------------------------===//
#include "mlir/Transforms/LowerAffine.h"
#include "mlir/AffineOps/AffineOps.h"
#include "mlir/Dialect/LoopOps/LoopOps.h"
#include "mlir/IR/AffineExprVisitor.h"
#include "mlir/IR/BlockAndValueMapping.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/IntegerSet.h"
#include "mlir/IR/MLIRContext.h"
#include "mlir/Pass/Pass.h"
#include "mlir/StandardOps/Ops.h"
#include "mlir/Support/Functional.h"
#include "mlir/Transforms/DialectConversion.h"
#include "mlir/Transforms/Passes.h"
using namespace mlir;
namespace {
// Visit affine expressions recursively and build the sequence of operations
// that correspond to it. Visitation functions return an Value of the
// expression subtree they visited or `nullptr` on error.
class AffineApplyExpander
: public AffineExprVisitor<AffineApplyExpander, Value *> {
public:
// This internal class expects arguments to be non-null, checks must be
// performed at the call site.
AffineApplyExpander(OpBuilder &builder, ArrayRef<Value *> dimValues,
ArrayRef<Value *> symbolValues, Location loc)
: builder(builder), dimValues(dimValues), symbolValues(symbolValues),
loc(loc) {}
template <typename OpTy> Value *buildBinaryExpr(AffineBinaryOpExpr expr) {
auto lhs = visit(expr.getLHS());
auto rhs = visit(expr.getRHS());
if (!lhs || !rhs)
return nullptr;
auto op = builder.create<OpTy>(loc, lhs, rhs);
return op.getResult();
}
Value *visitAddExpr(AffineBinaryOpExpr expr) {
return buildBinaryExpr<AddIOp>(expr);
}
Value *visitMulExpr(AffineBinaryOpExpr expr) {
return buildBinaryExpr<MulIOp>(expr);
}
// Euclidean modulo operation: negative RHS is not allowed.
// Remainder of the euclidean integer division is always non-negative.
//
// Implemented as
//
// a mod b =
// let remainder = srem a, b;
// negative = a < 0 in
// select negative, remainder + b, remainder.
Value *visitModExpr(AffineBinaryOpExpr expr) {
auto rhsConst = expr.getRHS().dyn_cast<AffineConstantExpr>();
if (!rhsConst) {
emitError(
loc,
"semi-affine expressions (modulo by non-const) are not supported");
return nullptr;
}
if (rhsConst.getValue() <= 0) {
emitError(loc, "modulo by non-positive value is not supported");
return nullptr;
}
auto lhs = visit(expr.getLHS());
auto rhs = visit(expr.getRHS());
assert(lhs && rhs && "unexpected affine expr lowering failure");
Value *remainder = builder.create<RemISOp>(loc, lhs, rhs);
Value *zeroCst = builder.create<ConstantIndexOp>(loc, 0);
Value *isRemainderNegative =
builder.create<CmpIOp>(loc, CmpIPredicate::SLT, remainder, zeroCst);
Value *correctedRemainder = builder.create<AddIOp>(loc, remainder, rhs);
Value *result = builder.create<SelectOp>(loc, isRemainderNegative,
correctedRemainder, remainder);
return result;
}
// Floor division operation (rounds towards negative infinity).
//
// For positive divisors, it can be implemented without branching and with a
// single division operation as
//
// a floordiv b =
// let negative = a < 0 in
// let absolute = negative ? -a - 1 : a in
// let quotient = absolute / b in
// negative ? -quotient - 1 : quotient
Value *visitFloorDivExpr(AffineBinaryOpExpr expr) {
auto rhsConst = expr.getRHS().dyn_cast<AffineConstantExpr>();
if (!rhsConst) {
emitError(
loc,
"semi-affine expressions (division by non-const) are not supported");
return nullptr;
}
if (rhsConst.getValue() <= 0) {
emitError(loc, "division by non-positive value is not supported");
return nullptr;
}
auto lhs = visit(expr.getLHS());
auto rhs = visit(expr.getRHS());
assert(lhs && rhs && "unexpected affine expr lowering failure");
Value *zeroCst = builder.create<ConstantIndexOp>(loc, 0);
Value *noneCst = builder.create<ConstantIndexOp>(loc, -1);
Value *negative =
builder.create<CmpIOp>(loc, CmpIPredicate::SLT, lhs, zeroCst);
Value *negatedDecremented = builder.create<SubIOp>(loc, noneCst, lhs);
Value *dividend =
builder.create<SelectOp>(loc, negative, negatedDecremented, lhs);
Value *quotient = builder.create<DivISOp>(loc, dividend, rhs);
Value *correctedQuotient = builder.create<SubIOp>(loc, noneCst, quotient);
Value *result =
builder.create<SelectOp>(loc, negative, correctedQuotient, quotient);
return result;
}
// Ceiling division operation (rounds towards positive infinity).
//
// For positive divisors, it can be implemented without branching and with a
// single division operation as
//
// a ceildiv b =
// let negative = a <= 0 in
// let absolute = negative ? -a : a - 1 in
// let quotient = absolute / b in
// negative ? -quotient : quotient + 1
Value *visitCeilDivExpr(AffineBinaryOpExpr expr) {
auto rhsConst = expr.getRHS().dyn_cast<AffineConstantExpr>();
if (!rhsConst) {
emitError(loc) << "semi-affine expressions (division by non-const) are "
"not supported";
return nullptr;
}
if (rhsConst.getValue() <= 0) {
emitError(loc, "division by non-positive value is not supported");
return nullptr;
}
auto lhs = visit(expr.getLHS());
auto rhs = visit(expr.getRHS());
assert(lhs && rhs && "unexpected affine expr lowering failure");
Value *zeroCst = builder.create<ConstantIndexOp>(loc, 0);
Value *oneCst = builder.create<ConstantIndexOp>(loc, 1);
Value *nonPositive =
builder.create<CmpIOp>(loc, CmpIPredicate::SLE, lhs, zeroCst);
Value *negated = builder.create<SubIOp>(loc, zeroCst, lhs);
Value *decremented = builder.create<SubIOp>(loc, lhs, oneCst);
Value *dividend =
builder.create<SelectOp>(loc, nonPositive, negated, decremented);
Value *quotient = builder.create<DivISOp>(loc, dividend, rhs);
Value *negatedQuotient = builder.create<SubIOp>(loc, zeroCst, quotient);
Value *incrementedQuotient = builder.create<AddIOp>(loc, quotient, oneCst);
Value *result = builder.create<SelectOp>(loc, nonPositive, negatedQuotient,
incrementedQuotient);
return result;
}
Value *visitConstantExpr(AffineConstantExpr expr) {
auto valueAttr =
builder.getIntegerAttr(builder.getIndexType(), expr.getValue());
auto op =
builder.create<ConstantOp>(loc, builder.getIndexType(), valueAttr);
return op.getResult();
}
Value *visitDimExpr(AffineDimExpr expr) {
assert(expr.getPosition() < dimValues.size() &&
"affine dim position out of range");
return dimValues[expr.getPosition()];
}
Value *visitSymbolExpr(AffineSymbolExpr expr) {
assert(expr.getPosition() < symbolValues.size() &&
"symbol dim position out of range");
return symbolValues[expr.getPosition()];
}
private:
OpBuilder &builder;
ArrayRef<Value *> dimValues;
ArrayRef<Value *> symbolValues;
Location loc;
};
} // namespace
// Create a sequence of operations that implement the `expr` applied to the
// given dimension and symbol values.
mlir::Value *mlir::expandAffineExpr(OpBuilder &builder, Location loc,
AffineExpr expr,
ArrayRef<Value *> dimValues,
ArrayRef<Value *> symbolValues) {
return AffineApplyExpander(builder, dimValues, symbolValues, loc).visit(expr);
}
// Create a sequence of operations that implement the `affineMap` applied to
// the given `operands` (as it it were an AffineApplyOp).
Optional<SmallVector<Value *, 8>> static expandAffineMap(
OpBuilder &builder, Location loc, AffineMap affineMap,
ArrayRef<Value *> operands) {
auto numDims = affineMap.getNumDims();
auto expanded = functional::map(
[numDims, &builder, loc, operands](AffineExpr expr) {
return expandAffineExpr(builder, loc, expr,
operands.take_front(numDims),
operands.drop_front(numDims));
},
affineMap.getResults());
if (llvm::all_of(expanded, [](Value *v) { return v; }))
return expanded;
return None;
}
// Given a range of values, emit the code that reduces them with "min" or "max"
// depending on the provided comparison predicate. The predicate defines which
// comparison to perform, "lt" for "min", "gt" for "max" and is used for the
// `cmpi` operation followed by the `select` operation:
//
// %cond = cmpi "predicate" %v0, %v1
// %result = select %cond, %v0, %v1
//
// Multiple values are scanned in a linear sequence. This creates a data
// dependences that wouldn't exist in a tree reduction, but is easier to
// recognize as a reduction by the subsequent passes.
static Value *buildMinMaxReductionSeq(Location loc, CmpIPredicate predicate,
ArrayRef<Value *> values,
OpBuilder &builder) {
assert(!llvm::empty(values) && "empty min/max chain");
auto valueIt = values.begin();
Value *value = *valueIt++;
for (; valueIt != values.end(); ++valueIt) {
auto cmpOp = builder.create<CmpIOp>(loc, predicate, value, *valueIt);
value = builder.create<SelectOp>(loc, cmpOp.getResult(), value, *valueIt);
}
return value;
}
// Emit instructions that correspond to the affine map in the lower bound
// applied to the respective operands, and compute the maximum value across
// the results.
Value *mlir::lowerAffineLowerBound(AffineForOp op, OpBuilder &builder) {
SmallVector<Value *, 8> boundOperands(op.getLowerBoundOperands());
auto lbValues = expandAffineMap(builder, op.getLoc(), op.getLowerBoundMap(),
boundOperands);
if (!lbValues)
return nullptr;
return buildMinMaxReductionSeq(op.getLoc(), CmpIPredicate::SGT, *lbValues,
builder);
}
// Emit instructions that correspond to the affine map in the upper bound
// applied to the respective operands, and compute the minimum value across
// the results.
Value *mlir::lowerAffineUpperBound(AffineForOp op, OpBuilder &builder) {
SmallVector<Value *, 8> boundOperands(op.getUpperBoundOperands());
auto ubValues = expandAffineMap(builder, op.getLoc(), op.getUpperBoundMap(),
boundOperands);
if (!ubValues)
return nullptr;
return buildMinMaxReductionSeq(op.getLoc(), CmpIPredicate::SLT, *ubValues,
builder);
}
namespace {
// Affine terminators are removed.
class AffineTerminatorLowering : public OpRewritePattern<AffineTerminatorOp> {
public:
using OpRewritePattern<AffineTerminatorOp>::OpRewritePattern;
PatternMatchResult matchAndRewrite(AffineTerminatorOp op,
PatternRewriter &rewriter) const override {
rewriter.replaceOpWithNewOp<loop::TerminatorOp>(op);
return matchSuccess();
}
};
class AffineForLowering : public OpRewritePattern<AffineForOp> {
public:
using OpRewritePattern<AffineForOp>::OpRewritePattern;
PatternMatchResult matchAndRewrite(AffineForOp op,
PatternRewriter &rewriter) const override {
Location loc = op.getLoc();
Value *lowerBound = lowerAffineLowerBound(op, rewriter);
Value *upperBound = lowerAffineUpperBound(op, rewriter);
Value *step = rewriter.create<ConstantIndexOp>(loc, op.getStep());
auto f = rewriter.create<loop::ForOp>(loc, lowerBound, upperBound, step);
f.region().getBlocks().clear();
rewriter.inlineRegionBefore(op.region(), f.region(), f.region().end());
rewriter.replaceOp(op, {});
return matchSuccess();
}
};
class AffineIfLowering : public OpRewritePattern<AffineIfOp> {
public:
using OpRewritePattern<AffineIfOp>::OpRewritePattern;
PatternMatchResult matchAndRewrite(AffineIfOp op,
PatternRewriter &rewriter) const override {
auto loc = op.getLoc();
// Now we just have to handle the condition logic.
auto integerSet = op.getIntegerSet();
Value *zeroConstant = rewriter.create<ConstantIndexOp>(loc, 0);
SmallVector<Value *, 8> operands(op.getOperation()->getOperands());
auto operandsRef = llvm::makeArrayRef(operands);
// Calculate cond as a conjunction without short-circuiting.
Value *cond = nullptr;
for (unsigned i = 0, e = integerSet.getNumConstraints(); i < e; ++i) {
AffineExpr constraintExpr = integerSet.getConstraint(i);
bool isEquality = integerSet.isEq(i);
// Build and apply an affine expression
auto numDims = integerSet.getNumDims();
Value *affResult = expandAffineExpr(rewriter, loc, constraintExpr,
operandsRef.take_front(numDims),
operandsRef.drop_front(numDims));
if (!affResult)
return matchFailure();
auto pred = isEquality ? CmpIPredicate::EQ : CmpIPredicate::SGE;
Value *cmpVal =
rewriter.create<CmpIOp>(loc, pred, affResult, zeroConstant);
cond =
cond ? rewriter.create<AndOp>(loc, cond, cmpVal).getResult() : cmpVal;
}
cond = cond ? cond
: rewriter.create<ConstantIntOp>(loc, /*value=*/1, /*width=*/1);
bool hasElseRegion = !op.elseRegion().empty();
auto ifOp = rewriter.create<loop::IfOp>(loc, cond, hasElseRegion);
rewriter.inlineRegionBefore(op.thenRegion(), &ifOp.thenRegion().back());
ifOp.thenRegion().back().erase();
if (hasElseRegion) {
rewriter.inlineRegionBefore(op.elseRegion(), &ifOp.elseRegion().back());
ifOp.elseRegion().back().erase();
}
// Ok, we're done!
rewriter.replaceOp(op, {});
return matchSuccess();
}
};
// Convert an "affine.apply" operation into a sequence of arithmetic
// operations using the StandardOps dialect.
class AffineApplyLowering : public OpRewritePattern<AffineApplyOp> {
public:
using OpRewritePattern<AffineApplyOp>::OpRewritePattern;
virtual PatternMatchResult
matchAndRewrite(AffineApplyOp op, PatternRewriter &rewriter) const override {
auto maybeExpandedMap =
expandAffineMap(rewriter, op.getLoc(), op.getAffineMap(),
llvm::to_vector<8>(op.getOperands()));
if (!maybeExpandedMap)
return matchFailure();
rewriter.replaceOp(op, *maybeExpandedMap);
return matchSuccess();
}
};
// Apply the affine map from an 'affine.load' operation to its operands, and
// feed the results to a newly created 'std.load' operation (which replaces the
// original 'affine.load').
class AffineLoadLowering : public OpRewritePattern<AffineLoadOp> {
public:
using OpRewritePattern<AffineLoadOp>::OpRewritePattern;
virtual PatternMatchResult
matchAndRewrite(AffineLoadOp op, PatternRewriter &rewriter) const override {
// Expand affine map from 'affineLoadOp'.
SmallVector<Value *, 8> indices(op.getIndices());
auto maybeExpandedMap =
expandAffineMap(rewriter, op.getLoc(), op.getAffineMap(), indices);
if (!maybeExpandedMap)
return matchFailure();
// Build std.load memref[expandedMap.results].
rewriter.replaceOpWithNewOp<LoadOp>(op, op.getMemRef(), *maybeExpandedMap);
return matchSuccess();
}
};
// Apply the affine map from an 'affine.store' operation to its operands, and
// feed the results to a newly created 'std.store' operation (which replaces the
// original 'affine.store').
class AffineStoreLowering : public OpRewritePattern<AffineStoreOp> {
public:
using OpRewritePattern<AffineStoreOp>::OpRewritePattern;
virtual PatternMatchResult
matchAndRewrite(AffineStoreOp op, PatternRewriter &rewriter) const override {
// Expand affine map from 'affineStoreOp'.
SmallVector<Value *, 8> indices(op.getIndices());
auto maybeExpandedMap =
expandAffineMap(rewriter, op.getLoc(), op.getAffineMap(), indices);
if (!maybeExpandedMap)
return matchFailure();
// Build std.store valutToStore, memref[expandedMap.results].
rewriter.replaceOpWithNewOp<StoreOp>(op, op.getValueToStore(),
op.getMemRef(), *maybeExpandedMap);
return matchSuccess();
}
};
// Apply the affine maps from an 'affine.dma_start' operation to each of their
// respective map operands, and feed the results to a newly created
// 'std.dma_start' operation (which replaces the original 'affine.dma_start').
class AffineDmaStartLowering : public OpRewritePattern<AffineDmaStartOp> {
public:
using OpRewritePattern<AffineDmaStartOp>::OpRewritePattern;
virtual PatternMatchResult
matchAndRewrite(AffineDmaStartOp op,
PatternRewriter &rewriter) const override {
SmallVector<Value *, 8> operands(op.getOperands());
auto operandsRef = llvm::makeArrayRef(operands);
// Expand affine map for DMA source memref.
auto maybeExpandedSrcMap = expandAffineMap(
rewriter, op.getLoc(), op.getSrcMap(),
operandsRef.drop_front(op.getSrcMemRefOperandIndex() + 1));
if (!maybeExpandedSrcMap)
return matchFailure();
// Expand affine map for DMA destination memref.
auto maybeExpandedDstMap = expandAffineMap(
rewriter, op.getLoc(), op.getDstMap(),
operandsRef.drop_front(op.getDstMemRefOperandIndex() + 1));
if (!maybeExpandedDstMap)
return matchFailure();
// Expand affine map for DMA tag memref.
auto maybeExpandedTagMap = expandAffineMap(
rewriter, op.getLoc(), op.getTagMap(),
operandsRef.drop_front(op.getTagMemRefOperandIndex() + 1));
if (!maybeExpandedTagMap)
return matchFailure();
// Build std.dma_start operation with affine map results.
rewriter.replaceOpWithNewOp<DmaStartOp>(
op, op.getSrcMemRef(), *maybeExpandedSrcMap, op.getDstMemRef(),
*maybeExpandedDstMap, op.getNumElements(), op.getTagMemRef(),
*maybeExpandedTagMap, op.getStride(), op.getNumElementsPerStride());
return matchSuccess();
}
};
// Apply the affine map from an 'affine.dma_wait' operation tag memref,
// and feed the results to a newly created 'std.dma_wait' operation (which
// replaces the original 'affine.dma_wait').
class AffineDmaWaitLowering : public OpRewritePattern<AffineDmaWaitOp> {
public:
using OpRewritePattern<AffineDmaWaitOp>::OpRewritePattern;
virtual PatternMatchResult
matchAndRewrite(AffineDmaWaitOp op,
PatternRewriter &rewriter) const override {
// Expand affine map for DMA tag memref.
SmallVector<Value *, 8> indices(op.getTagIndices());
auto maybeExpandedTagMap =
expandAffineMap(rewriter, op.getLoc(), op.getTagMap(), indices);
if (!maybeExpandedTagMap)
return matchFailure();
// Build std.dma_wait operation with affine map results.
rewriter.replaceOpWithNewOp<DmaWaitOp>(
op, op.getTagMemRef(), *maybeExpandedTagMap, op.getNumElements());
return matchSuccess();
}
};
} // end namespace
void mlir::populateAffineToStdConversionPatterns(
OwningRewritePatternList &patterns, MLIRContext *ctx) {
RewriteListBuilder<AffineApplyLowering, AffineDmaStartLowering,
AffineDmaWaitLowering, AffineLoadLowering,
AffineStoreLowering, AffineForLowering, AffineIfLowering,
AffineTerminatorLowering>::build(patterns, ctx);
}
namespace {
class LowerAffinePass : public FunctionPass<LowerAffinePass> {
void runOnFunction() override {
OwningRewritePatternList patterns;
populateAffineToStdConversionPatterns(patterns, &getContext());
ConversionTarget target(getContext());
target.addLegalDialect<loop::LoopOpsDialect, StandardOpsDialect>();
if (failed(
applyPartialConversion(getFunction(), target, std::move(patterns))))
signalPassFailure();
}
};
} // namespace
/// Lowers If and For operations within a function into their lower level CFG
/// equivalent blocks.
FunctionPassBase *mlir::createLowerAffinePass() {
return new LowerAffinePass();
}
static PassRegistration<LowerAffinePass>
pass("lower-affine",
"Lower If, For, AffineApply operations to primitive equivalents");